Conventionally, an image processing system has been used, in which an image forming apparatus and image reading apparatus are connected to an image processing controller connected to a PDL controller through a command I/F and Video I/F. The PDL controller creates raster image data by rasterizing each page of a print job described in PDL into an image. The command I/F serves to exchange commands. The Video I/F serves to exchange video image data.
The PDL controller interprets a PDL job received from a host computer connected through a network or the like to form a raster image, and sends a command sequence generated on the basis of the analysis result to the image processing controller through the command I/F. The PDL controller then sends the image data to the image processing controller through the Video I/F.
The image processing controller starts the image forming apparatus to form an image on a paper medium on the basis of the received command sequence and image data, and then output the paper medium outside the apparatus (see, for example, Japanese Patent Laid-Open Nos. 8-272555, 10-171617, and 11-240211).
In this conventional image processing system, image data is transferred by using the Video I/F, which is an image transfer path, regardless of the type of job to be processed. This Video I/F is exclusively designed for the transfer of uncompressed raster image data. When the image forming apparatus is a color printer, the Video I/F is designed to transfer 8-bit CMYK (four colors) signals per pixel in synchronism with an image clock. The data transfer rate of the Video I/F can be sufficiently increased in accordance with the engine speed. This I/F, however, requires dedicated hardware and its control mechanism, and hence leads to an increase in cost.
In addition, the transfer of image data occupies the Video I/F regardless of the type of image. Therefore, the next job cannot be transferred unless the transfer of the previous job is completed, even if the job does not require high image quality or is designed to print a black-and-white image by using an image forming apparatus capable of color printing. That is, the dedicated hardware is not effectively used.